Micro ajax wrapper in vanilla JS

http.js

  /**
   * Micro-wrapper for HTTP requests
   *
   * @type {Object}
   */
  window.http = {

    /**
     * Builds a valid URL. Unless a full URL (including a protocol) is given, the current origin will be used.
     *
     * @param   {String} uri    Request URI.
     * @param   {Object} params Query params as key-value pairs.
     * @returns {URL}           URL instance.
     * @private
     */
    _buildUrl ( uri, params ) {
      const url = uri.match( /^([a-z]+):\/\// ) ? new URL( '', uri ) : new URL( uri, window.location.origin );

      for ( let [ key, value ] of Object.entries( params ) ) {
        if ( Array.isArray( value ) ) {
          for ( let item of value ) {
            url.searchParams.append( `${key}[]`, encodeURIComponent( item ) );
          }

          continue;
        }

        url.searchParams.append( key, encodeURIComponent( value ) );
      }

      return url;
    },

    /**
     * Assigns the defaults headers and any additional headers
     *
     * @param   {Object} additionalHeaders
     * @returns {Headers}
     * @private
     */
    _buildHeaders ( additionalHeaders = {} ) {
      return new Headers(
        Object.assign(
          {},
          additionalHeaders,
          {
            // Set the content type to JSON
            'Content-Type': 'application/json',

            // Include the API token
            Authorization: `Bearer ${window.api_token}`,

            // Include the CSRF token
            'X-CSRF-Token': window.csrf_token
          }
        )
      );
    },

    /**
     * Holds all methods that can carry a request body
     *
     * @type {String[]}
     * @private
     */
    _methodsWithBody: [
      'POST',
      'PUT',
      'PATCH'
    ],

    /**
     * Requests a resource
     *
     * @param   {Object}                                           [options]         Request options
     * @param   {String}                                           [options.uri]     Request URI, defaults to "/"
     * @param   {Object}                                           [options.params]  URL query params, defaults to {}
     * @param   {String}                                           [options.method]  Request method, defaults to "GET"
     * @param   {Object}                                           [options.headers] Request headers, defaults to {}
     * @param   {Object}                                           [options.body]    Optional request body, defaults to {}
     * @returns {Promise<Array|Object|String|Boolean|Number|null>}                   Parsed response data
     */
    async request ( options = {} ) {

      // Build the URL
      const url = this._buildUrl(
        options.hasOwnProperty( 'uri' ) ? options.uri : '/',
        options.hasOwnProperty( 'params' ) ? options.params : {}
      );

      // Create the basic request options
      const requestOptions = {
        method:  options.hasOwnProperty( 'method' ) ? options.method.toUpperCase() : 'GET',
        headers: this._buildHeaders( options.hasOwnProperty( 'headers' ) ? options.headers : {} )
      };

      // If this is a method with a body, include any body now
      if ( this._methodsWithBody.includes( requestOptions.method ) ) {
        requestOptions.body = typeof options.body === 'string'
                              ? options.body
                              : JSON.stringify( typeof options.body !== 'undefined' ? options.body : {} );
      }

      // Fetch the response async
      const response = await fetch( url, requestOptions );

      // If something has gone wrong, create a helpful error
      if ( !response.ok ) {
        throw new Error( `${options.method} Request failed [${response.status}]: ` + await response.text() );
      }

      // Return the response JSON promise
      return response.json();
    },

    /**
     * Performs an HTTP GET request.
     *
     * @param   {String}          [uri]     Request URL. May be relative to the origin.
     * @param   {Object}          [params]  Request query parameters as key-value pairs.
     * @param   {Object}          [headers] Request headers as key-value pairs.
     * @returns {Promise<Array|Object|String|Boolean|Number|null>}
     */
    async get ( uri = apiPrefix, params = {}, headers = {} ) {
      return this.request( { method: 'GET', uri, params, headers } );
    },

    /**
     * Performs an HTTP HEAD request.
     *
     * @param   {String}          [uri]     Request URL. May be relative to the origin.
     * @param   {Object}          [params]  Request query parameters as key-value pairs.
     * @param   {Object}          [headers] Request headers as key-value pairs.
     * @returns {Promise<Array|Object|String|Boolean|Number|null>}
     */
    async head ( uri = apiPrefix, params = {}, headers = {} ) {
      return this.request( { method: 'HEAD', uri, params, headers } );
    },

    /**
     * Performs an HTTP DELETE request.
     *
     * @param   {String}            [uri]     Request URL. May be relative to the origin.
     * @param   {Object}            [params]  Request query parameters as key-value pairs.
     * @param   {Object}            [headers] Request headers as key-value pairs.
     * @returns {Promise<Array|Object|String|Boolean|Number|null>}
     */
    async delete ( uri = apiPrefix, params = {}, headers = {} ) {
      return this.request( { method: 'DELETE', uri, params, headers } );
    },

    /**
     * Performs an HTTP POST request.
     *
     * @param   {String}            [uri]     Request URL. May be relative to the origin.
     * @param   {Object|String}     [body]    Request body data. Will be converted to JSON.
     * @param   {Object}            [params]  Request query parameters as key-value pairs.
     * @param   {Object}            [headers] Request headers as key-value pairs.
     * @returns {Promise<Array|Object|String|Boolean|Number|null>}
     */
    async post ( uri = apiPrefix, body = {}, params = {}, headers = {} ) {
      return this.request( { method: 'POST', uri, params, body, headers } );
    },

    /**
     * Performs an HTTP PUT request.
     *
     * @param   {String}            [uri]     Request URL. May be relative to the origin.
     * @param   {Object|String}     [body]    Request body data. Will be converted to JSON.
     * @param   {Object}            [params]  Request query parameters as key-value pairs.
     * @param   {Object}            [headers] Request headers as key-value pairs.
     * @returns {Promise<Array|Object|String|Boolean|Number|null>}
     */
    put ( uri = apiPrefix, body = {}, params = {}, headers = {} ) {
      return this.request( { method: 'PUT', uri, params, body, headers } );
    },

    /**
     * Performs an HTTP PATCH request.
     *
     * @param   {String}            [uri]     Request URL. May be relative to the origin.
     * @param   {Object|String}     [body]    Request body data. Will be converted to JSON.
     * @param   {Object}            [params]  Request query parameters as key-value pairs.
     * @param   {Object}            [headers] Request headers as key-value pairs.
     * @returns {Promise<Array|Object|String|Boolean|Number|null>}
     */
    async patch ( uri = apiPrefix, body = {}, params = {}, headers = {} ) {
      return this.request( { method: 'PATCH', uri, params, body, headers } );
    }
  };